The subject matter of the present invention is a continuous inkjet printing arrangement comprising a single nozzle continuous inkjet printhead provided with heating means, an ink supply line connecting an ink source to the printhead and returning gutter ink from the printhead to the ink source, a filter in said supply line and ink supply management means for controlling the supply of ink to the said printhead.
It is known (U.S. Pat. No. 3,999,190) that the viscosity of the ink just prior to dispersement from the printing head must be accurately controlled in order to maintain proper droplet formation, and that heating the printhead to a preselected temperature permits to accurately control the viscosity. It is also known (U.S. Pat. No. 4,106,030) that a continuous inkjet printhead must be supplied with filtered ink.
However the viscosity of inks intended to be applied to continuous inkjet printing arrangements still remains an important problem in the inkjet printing technology, particularly in view of the fact that there is an increasing interest in printing inks containing a high loading of pigment, for example inks containing chemically or thermodynamically stabilised pigments, high abrasive and high-density inorganic pigments, or inks that contain security features such as fluorescent pigments.
The aim of the present invention is to propose a continuous inkjet printer arrangement able to be used advantageously for printing inks of the above mentioned type.
To this end the present invention relates to a continuous inkjet printer arrangement comprising a single nozzle continuous inkjet printhead provided with heating means, an ink supply line connecting an ink source to the printhead and returning gutter ink from the printhead to the ink source, a filter in said supply line and ink supply management means for controlling the supply of ink to the said printhead, wherein the filter is provided with heating means and the ink supply management means are arranged for continuously maintaining in said filter a temperature higher than elsewhere in the ink supply and for maintaining said printhead at a constant temperature higher than the ambient temperature.
The filter may be located in a metal housing containing an electrical heating element. In particular, the filter may be located between two metal plates one of which is provided with a heating means.
At least five static mixers may be incorporated at strategic points within the system, where two static mixers may be incorporated in said ink supply line, one of which is located immediately upstream of said filter, the other being located immediately downstream of said filter.
According to an embodiment, the filter may be mounted immediately adjacent to the printhead.
According to another embodiment, the ink supply line may be connected to at least one element of the ink supply management system between the downstream end of the static mixer following the filter and the inlet of the printhead.
The static mixers in the ink supply line may be heated.